Preliminary results on limestone weathering caused by air pollution and microbial colonization are presented in this study. Outdoor exposure experimental assays were performed on Scaglia limestone samples. Samples were exposed in two areas in Perugia (Italy) that differ in degree of urban air pollution. At different times of exposure, ranging from 1 to 12 months, microbial contamination of sampled surfaces was evaluated by microbiological techniques, genotyping and scanning electron microscopy. After 1 year of exposure, a significant fungal colonization and the presence of weathering products (i.e., gypsum) were detected on sampled surfaces.